Surface Probes

Single-Pass Crack
Detection in Gears

Gears are critical components in a variety of mining equipment, such as girth gears, pinions, bull gears, and sugar mill drive trains. For safety and life-cycle considerations each gear must be closely monitored for surface-breaking cracks caused by stress during operation.

Techniques such as dye-penetrant testing (PT) and magnetic particle testing (MT) are the conventional inspection methods on gears, making them expensive and time consuming.

Faster and Better Sensitivity

By design, eddy current array (ECA) is more sensitive to small surface defects than magnetic particle testing (MT), penetrant testing (PT), and ultrasonic testing (UT) because of the way eddy currents propagate inside conductive materials, such as those in gears. PT, MT, and UT also require extensive pre-inspection (surfaces must be free of lubricant) and post-inspection (lubricant must be reapplied at the end of the inspection) processing. Multiplexing an array of eddy current testing (ECT) coils allows scanning wider surfaces faster than other techniques or pencil ECT probes could, enabling scanning gear tooth flanks in a single pass.

Computerized Records

ECA gives the acquisition and analysis software the ability to display inspection data from gears in the form of 2D and 3D C-scans. C-scans obtained with ECA technology are much simpler to analyze and much more accurate than other display methods. These scans can easily be recorded and reported on, which are also great advantages over other inspection technologies.

Standard-Quality Inspection

ECA complies the ASNT E2905 Standard Practice for Examination of Mill and Kiln Girth Gear Teeth—Electromagnetic Methods for inspecting gears, ensuring quality results.

High Liftoff Tolerance

Tooth profile shapes and sizes in gears vary greatly and require profiled probes that can minimize liftoff, which increases probe sensitivity.

Rugged and Easy to Handle

ECA probes for gears are ingeniously equipped with silicon-nitride ceramic balls to minimize wear. The probe’s shape also makes handling easier, even with gloves.

Eddy current array probe for gears on test component



  • Small
  • Medium
  • Large

Gear modules

  • Small: 13–20
  • Medium: 20–30
  • Large: 30–42


Long, single driver


3 m (9.8 ft)


  • Small: 50 mm (2.0 in)
  • Medium: 76 mm (3.0 in)
  • Large: 112 mm (4.4 in)

Central frequency

500 kHz

Frequency range

250 kHz–1 MHz

Coils (diameter×number)

  • Small: 4.5 mm × 22
  • Medium: 4.5 mm × 33
  • Large: 4.5 mm × 48

Minimum channel requirement

  • Small: 32, 64
  • Medium: 64
  • Large: 96